code: def test_doc(self):
      self.assertEqual(sentinel("a", "b").__doc__, "b")
  
file_path: catalyst/tests/utils/test_sentinel.py
imports: from copy import copy, deepcopy
  from pickle import loads, dumps
  from unittest import TestCase
  from weakref import ref
  from catalyst.utils.sentinel import sentinel
label_desc: Use image node_id 3 for calling the SentinelTestCase obj's underlying member method code with example usage: obj.test_doc() without return types